There are several prior processes for the preparation of calcium borate both from boric acid and from minerals, which contain borate salts, such as ulexite.
The specific treatment process, depends on the type of mineral used, its purity (impurity contents), and "grade" (percentage of borate contained in the minerals), as well as on the desired quality of calcium borate to be produced.
The basic process for the production of boric acid, as noted in the Kirk Othmer encyclopedia of Chemical Technology, 2nd edition, 1964,, vol. 3, page 615, starts from the reaction of colemanite with sulfuric acid.
A classic example for the formation of boron and calcium compounds from boric acid, cited in the Kirk Othmer encyclopedia of Chemical Technology, 2nd edition, 1964, vol. 3, page 649, makes reference to the formation of calcium-boron compounds (CaO/B.sub.2 0.sub.3, molar ratio 1:3) by reacting boric acid and calcium acetate.
The most frequent examples of processes for the production of calcium borate are those which start with ulexite, (Na.sub.2 0.2CaO.5B.sub.2 0.sub.3.16H.sub.2 0).
One such process is that disclosed by Eastes in U.S. Pat. No. 4,270,944, assigned to Owens Corning Fiberglass, wherein a high quality ulexite (from Borates of Peru, having an oxide composition of 6.9% Na.sub.2 0, 9.9% CaO and 41.8% B.sub.2 0.sub.3) is primarily dissolved in hot hydrochloric acid to form a mixture containing undissolved solids. This mixture is filtered. Calcium chloride is added to the solution to replace all sodium in the ulexite. Said solution is neutralized with sodium hydroxide, at a pH of from 7 to 9, to form a white, calcium borate precipitate which is filtered, washed with water, and dried at 110.degree. C. for 2 or 3 hours. This process yields a calcium borate containing from 46.7% to 49% B.sub.2 0.sub.3.
Another recent example is the cyclic process for obtaining calcium borate and sodium borate as disclosed by Pepi in U.S. Pat. No. 5,268,154, assigned to Bitossi Dianella S.P.A. This process comprises the disaggregation of ulexite in a liquid containing H.sub.3 BO.sub.3 and Na.sub.2 0 at a temperature of from 120.degree. C. to 200.degree. C., to form a suspension. Calcium borate, with the formula 4CaO.5B.sub.2 0.sub.3.7H.sub.2 0, is recovered from the suspension by hot filtration. Sodium borate dehydrate is crystallized from the remaining liquid, at a temperature of 30.degree. C., and separated from the mother liquor. Sodium hydroxide is added to the mother liquor to maintain the weight ratio of H.sub.3 BO.sub.3 /Na.sub.2 0 between 1.8 and 2.7. The mother liquor with NaOH is recycled for use as part of the disaggregation liquid.
In U.S. Pat. No. 3,332,738, 1967, assigned to the U.S. Navy Department, Wieder et al disclosed a method for the production of synthetic colemanite in which sodium borate or boric acid are reacted with compounds such as Ca(I0.sub.3).sub.2, CaCl.sub.2, Ca(C.sub.2 H.sub.3 0.sub.2).sub.2 for from 1 to 8 days.
Other patents for processes for the production of boric acid, include:
1. U.S. Pat. No. 2,020,570 issued to Solvay Et Cie, wherein calcined colemanite suspended in water is reacted with C0.sub.2 in a reactor at a high pressure; PA1 2. U.S. Pat. No. 4,196,177, wherein an alkaline borate is reacted with ammonia and ammonium sulfite in the presence of methanol. PA1 3. U.S. Pat. No. 3,650,690 issued to Stauffer Chemical, wherein an alkaline borate is reacted with sulfuric acid, and subsequently, with overheated vapor, boric acid is vaporized and recovered. PA1 4. Other patents disclose the attack of boron and calcium or boron and sodium minerals with the following reagents: hydrochloric acid (U.S. Pat. No. 2,855,276), phosphoric acid (British patent No 423,293), ammonium carbonate (Switzerland patent No. 354,760). PA1 5. U.S. Pat. No. 2,089,406, assigned to Pacific Coast Borax Co. shows the production of boric acid from rasorite (Na.sub.2 O.2B.sub.2 O.sub.3.4H.sub.2 O) with sulfuric acid; and
6. U.S. Pat. 3,103,412 assigned to Tholand, Inc., wherein the colemanite and/or howlite mineral is reacted with ammonium sulfate.
Additionally, as illustrated in the papers Bulltech University Istanbul, vol. 38, page 207-231, 1985; Journal of Colloid Science, vol. 13, page 386-396, Journal of Crystal Growth, vol. 20, pages 125-134, 1973, Can. J. Chem. vol. 36, pages 1057-1063, 1958, in the production boric acid, prior to the production of calcium borate, the proper formation of gypsum, which is one of the reaction products of colemanite with sulfuric acid, is of great importance.
As can be seen, the production of boric acid can be started from a variety of boron and calcium and/or boron and sodium minerals and/or compounds, using various agents and reaction conditions.
A bibliographic search found processes for beneficiating colemanite and /or howlite utilizing both mechanical methods, such as grinding, attrition and separation, and chemical methods, such as chemical reactions, solvent extraction or calcination. However, colemanite and/or howlite minerals that are contaminated with arsenic, iron, magnesium, strontium, silica, sulfates, among other contaminants are inappropriate for beneficiating where the compound of calcium-boron obtained remain in favorable conditions for an industrial use without damaging equipment and/or measurement systems.
Examples of processes for beneficiating colemanite and/or howlite, are represented by U.S. Pat Nos. 4,756,745, 4,756,894 and 4,804,524, issued to Polendo and assigned to Materias Primas Magdalena. In the first two, colemanite and/or howlite minerals are reacted firstly with sulfuric acid to form a solution from which the solids are removed as a gypsum cake and the remaining solution is reacted with sulfhydric acid (H.sub.2 S), to precipitate arsenic and iron impurities, to produce a beneficiated colemanite or boric acid, with a lower amount of impurities. These patents also disclose the possibility of producing calcium borate by reacting the beneficiated colemanite with Ca(OH).sub.2. In the second mentioned patent, after the arsenic and iron impurities are precipitated with H.sub.2 S, the remaining solution is reacted with NH.sub.3, to precipitate aluminum impurities Al(OH).sub.3 and again with sulfuric acid to precipitate (NH.sub.4).sub.2 SO.sub.4, to obtain boric acid.
Since these processes start with colemanite and/or howlite minerals of low purity (high impurity content) and low "grade" (low content of borate in such minerals), it has always been considered strictly necessary to precipitate and remove the arsenic, iron, and ammonium sulfate impurities, to get an industrially acceptable beneficiated colemanite or boric acid .
In this invention low purity and low grade colemanite and/or howlite minerals are utilized without treatment of the strong liquor with reagents such sulfhydric acid (H.sub.2 S) and ammonia (NH.sub.3) to eliminate impurities.